A composite material of manganese oxide and Ketjen black (KB) was synthesized by a sonochemical method. The KB was expected to be both a support of the manganese oxide and a conducting additive of the composite material. To demonstrate that the composite is suitable for rapid discharge-charge, the composite material was tested at high current densities. The composite exhibited a 127 mAh g(-1) discharge capacity at a 50 A g(-1) current density. It means that this capacity could be discharged in 9 s. (C) 2005 The Electrochemical Society.